6739
J . Am. Chem. SOC.1985, 107, 6739-6740
formation with dibenzo- 18-crown-6 annd glycine hydrochloride but not glycine itself in MeOH. The only successful case involves phenylalanine transport in a photoactivated system.' The present cases suggest that suitable derivatives of 1 should permit recognition of other side chains and our current research is directed at this prospect.
Scheme I
+
(co)5w=c
RC=CH
(CO),W=C
I
\OCH,
R C E C H 'OCH,
2
1
/
Acknowledgment. We are grateful to the National Institutes of Health for financial support of this research. Ph
I I I
(CO),W-C-OMe
(7) Sunamoto, J.; Iwamoto, K.; Mohri, Y. J . Am. Chem. SOC.1982, 104, 5502-5504.
f=c\
R
Photoassisted Polymerization of Terminal Alkynes by W(CO)6 Involving Catalyst Generation by an Alkyne to Vinylidene Ligand Rearrangement Shayne J. Landon, Peter M. Shulman, and Gregory L. Geoffrey* Department of Chemistry The Pennsylvania State University University Park, Pennsylvania 16802 Received May 6, 1985 Katz and co-workers' have demonstrated that (CO),W(C(0Me)Ph) (1) catalyzes the polymerization of alkynes, and the mechanism of Scheme I which involves carbene-alkyne and metallacyclobutene intermediates has been implicated. We independently prepared the important alkyne-carbene intermediate 2 by low-temperature photolysis of 1 in the presence of alkynes and showed that it leads to alkyne polymerization upon warm-up.2 Herein we demonstrate that use of a preformed carbene complex is not necessary since active alkyne polymerization catalysts can be formed by photolysis of W(CO), with terminal alkynes in hydrocarbon solutions. A key step in the catalyst generation is rearrangement of a coordinated alkyne to a vinylidene ligand. Irradiation of W(CO), in the presence of alkynes has been reported to give unstable (CO)5W(q2-alkyne)c ~ m p l e x e s . ~We verified these earlier results with CH3C=CCH3, P h C S C P h , t-BuC==CH, P h C S C H , and HC=CH but also observed formation of large amounts of red poly(phenylacety1ene) (I) and black trans-poly(acety1ene) (11) in the latter two cases, eq l . 4 The W(CO),
+
+
C A R
hv -CO
RC=CH R=Ph. H
(CO)5W+II
c \ ~
+
(RC=CH),
/ (CO),W
Ph
I.R = P h
polymers were identified by their characteristic IR spectra and by a molecular weight measurement for (PhC=CH),, but the C, H analyses for both were persistently low, due to contamination by tungsten residues., These products were repeatedly observed (1) (a) Katz, T. J.; Ho, T. H.; Shih, N . Y.; Ying, Y. C.; Stuart, V. I . W. J . Am. Chem. SOC.1984, 106, 2659. (b) Katz, T. J.; Lee, S. J. J . Am. Chem. SOC.1980, 102, 422. (c) See also: Thoi, H. H.; Ivin, K. J.; Rooney, J. J. J . Chem. SOC.,Faraday Trans. 1 1982, 78, 2227. (2) Foley, H.; Strubinger, L. M.; Targos, T. S.; Geoffroy, G.L. J . Am. Chem. SOC.1983, 105, 3064. (3) Stolz, I. W.; Dobson, G. R.; Sheline, R. K. Inorg. Chem. 1963, 2, 1264. (4) A typical experiment involved photolysis (A > 300 nm) of a hexane solution (60 mL) of W(CO)6 (0,135 g, 0.32 mmol) and phenylacetylene (1.0 mL, 1.05 mmol) in a Schlenk flask at 25 OC for 24 h. Similar reaction conditions were employed for HC=--CH which was passed through a saturated NaHSOl solution to remove the acetone stabilizer. (5) (PhC=CH),: Anal. Calcd for (C8H6)x: C, 94.12; H , 5.88. Found: C, 86.57; H, 5.81. ' H NMR (CDCI,) 7.74 ppm (br, m);mol wt (osmometry, THF) 1815, 1757 (twosamples); IR (KBr) 697 s, 755 s, 1028 w, 1074 w, 1443 m, 1491 m, 3025 w, 3054 w cm-'. For a discussion of the IR spectra of (PhC=CH),, see, for example: Tsonis, C. P.; Farona, M. F. J . Polym. Sci., Polym. Chem. Ed. 1979, 17, 1779. Kern, R. J. Ibid. 1969, 7 , 621. Masuda, T.; Sasaki, N.; Higashimura, T. Macromolecules 1975, 8 , 717. trans(HC=CH),: IR (KBr) 2965 m, 1076 m br cm-'. For a discussion of the IR spectra of (HC=CH),, see: Kleist, F. D.; Byrd, N. R. J. Polym. Sci., Polym. Chem. Ed. 1969, 7, 3419. Watson, W. H.; McMordie, W. D.; Lands, L. G. J . Polym. Sei. 1961, 55, 137.
0002-7863/85/1507-6739$01 .50/0
Ph H
H
Ph
when either rigorously purified solvents, alkynes, and W(CO), or as-received materials were used. With HCECH, irradiation was only necessary to initiate the polymerization since it continued 90 h after cessation of photolysis with no sign of abatement. However, polymerization of P h C I C H ceased when irradiation was stopped. IR monitoring of the active catalyst solutions showed only the presence of W(CO), and (CO),W(q2-alkyne), and thus the active polymerization agent must be present in trace amounts and must be extremely active. In related work, Masuda et aL6 reported that polymerization occurred when W(CO), was irradiated with alkynes in halocarbon solvents. This polymerization may proceed by the generation of halocarbene complexes which catalyze the polymerization by the mechanism of Scheme I or by the route suggested below for W(CO)6 in hydrocarbon solutions. We suggest that irradiation of W(CO), with terminal alkynes in hydrocarbon sohents leads to the formation of catalytically active vinylidene complexes by rearrangement of the initially formed q2-alkyne complexes, eq 2.
(co),w=C=c
(1)
11.R = H
H
c\H
/
\
-*
-co
+RC=cH
H
3a. R = P h 3b, R = H R
\
k
I
FC\
R
H
Thermal or photochemical loss of CO from 3 and coordination of alkyne then allow entry into a catalytic cycle similar to that of Scheme I. The metal-assisted rearrangement of terminal alkynes to vinylidene ligands is now quite well established,' although the reaction has never been used for the present purpose. The proposed vinylidene intermediates 3a,b have not been reported although related vinylidene complexes (CO),M=C=CRR' (M = Cr, W) have been mentioned.s In one instance a vinylidene (6) (a) Masuda, T.; Kuwane, Y.; Yamamoto, K.; Higashimura, T.Polym. Bull. 1980, 2, 823. (b) Masuda, T.; Yamamoto, K.; Higashimura, K. Polymer 1982, 23, 1663. (c) Masuda, T.; Higashimura, T. Acc. Chem. Res. 1984, 17, 51. (7) (a) Bruce, M. I.; Swincer, A. G. Adc. Organomer. Chem. 1983.22, 59. (b) Birdwhistell, K. R.; Burgmayer, S. J. N.; Templeton, J. L. J . Am. Chem. SOC.1983, 105, 7789.
0 1985 American Chemical Society
6740
J . A m . Chem. SOC.1985, 107, 6140-6742
complex has been suggested to lead to alkyne dimerization. Berke and co-workers8a observed that addition of HC=CC02CH3 to solutions of photogenerated (CO),Cr{OEt,] gave the products of eq 3, with 4 and 5 proposed to arise via intermediacy of the vinylidene complex (CO),Cr=C=C(C02CH3)H.
occur upon heating (arene)M(CO), (M = Cr, Mo, W) with terminal alkynes.'*
Acknowledgment. This research was supported by the donors of the Petroleum Research Fund, administered by the American Chemical Society.
/C0ZCH3 ~~
(CO),CrpEt,)
+
HCECCO,CH,
-
d
+
(CO15Cr-l/I C
\\ H C0,CH3
1
CO,CH,
~~
~~~
~~
~
(12) Woon, P.S.; Farona, M. F. J . Polym. Sci., Polym. Chem. E d . 1974, 12, 1749. (13) In this paper the periodic group notation is in accord with recent actions by IUPAC and ACS nomenclature committees. A and B notation is eliminated because of wide confusion. Groups 1A and IIA become groups 1 and 2 . The d-transition elements comprise groups 3 through 12, and the p-block elements comprise groups 13 through 18. (Note that the former Roman number designation is preserved in the last digit of the new numbering: e.g., 111 3 and 13.)
-
I
C0,CH3 c
4
I .
To test the mechanistic suggestion of eq 2, we attempted to generate the proposed vinylidene intermediate 3a by protonation of [PPN] [(CO)5WC=CPh],9 a well-established route to vinylidene complexe~.'~~*~ This complex forms at -77 OC, but it rapidly decomposes upon warm-up. In contrast, the vinylidene complex (CO),W=C=(Me)-t-Bu ( 6 ) , which was recently prepared by Mayr et a1.8bby addition of [(CH,),O]BF, to [(CO)sWC=Ct-Bul-, can be isolated as a dark green oil. We repeated the preparation of 6 and found by IR monitoring that no reaction occurred between 6 and excess P h C E C H when these reagents were stirred together at 22 OC for 1 h. However, 366-nm photolysis induced an immediate reaction as evidenced by the rapid green to red color change and the deposition of red poly(phenylacetylene). Thus the vinylidene complex 6 is capable of affecting alkyne polymerization, presumably by loss of CO, coordination of alkyne, and then entry into the mechanism of Scheme I. By analogy, the vinylidene complex 3a should also initiate polymerization. In support of this suggestion, we find that complex 6 , like 1,* cleanly loses C O upon 366-nm irradiation in CH3CN solution to give UV and IR spectral changes indicative of formation of C~S-(CO),(CH~CN)W=C=C(~-BU)CH~.'~ Further evidence for the suggested mechanism comes from experiments with CH3C=CCH3. Both Katz' and we2 showed that poly(2-butyne) results when (C0)5W{C(OMe)Ph)is heated or irradiated in the presence of 2-butyne. However, unlike P h C S C H , 2-butyne cannot form a vinylidene complex upon interaction with photogenerated W(CO), since it does not have an acidic hydrogen. Consistent with the proposed vinylidene intermediate in our mechanism, photolysis of W(CO), in the presence of 2-butyne does not lead to polymer, but only to the q2-2-butynecomplex. However, when a trace of P h m H (
